CN111801304A

CN111801304A - cBN sintered body and cutting tool

Info

Publication number: CN111801304A
Application number: CN201980016596.5A
Authority: CN
Inventors: 矢野雅大; 小口史朗; 宫下庸介
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2018-03-14
Filing date: 2019-03-14
Publication date: 2020-10-20
Anticipated expiration: 2039-03-14
Also published as: CN111801304B; US11383305B2; JP2019156688A; US20210001411A1; WO2019177094A1; JP7015979B2; EP3766857A1; EP3766857A4

Abstract

The cBN sintered body of the invention is composed of cubic boron nitride particles and a ceramic binder phase, and has an average particle diameter of 10nm to 200nm WSi₂Is dispersed in the sintered body so that the content ratio thereof is 1 to 20 vol%. A cutting tool has the cBN sintered body as a tool base body.

Description

cBN sintered body and cutting tool

Technical Field

The present invention relates to a cubic boron nitride (hereinafter referred to as "cBN") based ultra-high pressure sintered body (hereinafter referred to as "cBN sintered body") having excellent toughness, and a cutting tool (hereinafter referred to as "cBN tool") using the same as a tool base.

The present application claims priority based on patent application No. 2018-047247 filed on japanese application No. 2018, 3, 14 and the content thereof is incorporated herein by reference.

Background

Heretofore, it has been known that a cBN sintered body is excellent in toughness and low in affinity with an iron-based material, and therefore, the cBN sintered body is widely used as a cutting tool material for an iron-based workpiece material such as steel or cast iron by effectively utilizing these characteristics.

For example, patent document 1 describes a cBN sintered body having the following configuration.

(a) Contains about 60 to 80 vol% of cBN having an average grain size of about 3 to 6 μm.

(b) The binder phase comprises about 40 to 20 volume percent of a ceramic binder phase, (i) about 20 to 60 volume percent of the ceramic binder phase is one or more carbides, nitrides, or borides of group IVA or group VIA metals, and (ii) about 40 to 80 volume percent of the ceramic binder phase is one or more carbides, nitrides, borides, or oxides of aluminum.

(c) About 3 to 15 wt% of tungsten, TiB₂Of [101 ]]Peak and WB [110 ]]The XRD intensity ratio of the peaks is less than about 0.4.

Further, the cBN sintered body described in patent document 2 has cubic boron nitride particles of 20 volume% or more and 80 volume% or less and a binder material composed of at least one selected from nitrides, carbides, borides, oxides and solid solutions of group IVB elements, group VB elements, group VIB elements of the periodic table, at least one selected from simple substances, compounds and solid solutions of Zr, Si, Hf, Ge, W, Co and compounds of Al, and when W and/or Co are contained in the composite sintered body, the total weight of W and/or Co is less than 2.0 weight% and any one or more of Zr, Si, Hf and Ge (hereinafter referred to as "X") is contained, each element of X is 0.005 weight% or more and less than 2.0 weight%, and X/(X + W + Co) satisfies 0.01 or more and 1.0 or less, and the weight of Al is 2.0-20.0 wt%.

Patent document 1: japanese laid-open patent application No. 2004-160637

Patent document 2: japanese patent No. 5189504

Since the cBN sintered body described in patent document 1 contains W in the sintered body, Ti boride (TiB) is produced simultaneously at the time of sintering₂) Phase and W Boride (WB) phase. The W boride phase produced suppresses the production of Ti boride phase at the cBN particle-binder phase interface, and TiB₂Of [101 ]]Peak and WB [110 ]]The XRD intensity ratio of the peak is suppressed to less than about 0.4. Therefore, the cBN particle-binder phase interface is deteriorated in adhesion, which becomes a starting point of crack generation, resulting in a problem that toughness and chipping resistance are deteriorated.

In the cBN sintered body described in patent document 2, in order to improve the strength and toughness of the binder phase, a predetermined amount of W and/or Co, Si or Zr is contained in the binder phase, but if the proportion of W in the sintered body is large, the toughness in the sintered body is lowered, and if Si is large, the diffusion reaction of the binder material is excessively suppressed, and the binding force between the cBN particles and the binder material and between the cBN particles and the binder material is lowered, resulting in a problem that the toughness of the sintered body is lowered. Further, when the dispersibility during mixing is poor, a portion having a high concentration of the additive locally occurs, and the toughness of the binder in this portion is lowered, and when the binder is used as a tool, the fracture resistance is lowered due to the occurrence of a starting point of fracture.

Disclosure of Invention

The present invention has been made to solve the problem of the conventional cBN sintered body that sufficient toughness cannot be secured, and an object of the present invention is to provide a cBN sintered body having high toughness and a cBN tool using the same as a tool base.

In order to solve the above problems, the present inventors have conducted studies on a cBN sintered body and a CBN tool using the same as a tool base, wherein dispersed particles are formed in the cBN sintered body so that the cBN particle-binder phase interface does not suffer from a decrease in adhesion even when a W compound is contained thereinThe study was conducted intensively. As a result, it was found that when particles that do not form a reaction product with cBN particles are dispersed, the formation of a Ti boride phase formed at the cBN particle-binder phase interface is not inhibited. Further, the following new findings are made: the particles are suitable for WSi₂Particles and WSi of a fine particle size in a specific average particle size range₂Particles are dispersed in the binder phase of the cBN sintered body, and even when cracks are generated in the sintered body, the progress of the cracks is progressed by WSi₂The sintered cBN is finely detoured, and the linear progress can be suppressed, whereby a sintered cBN having high toughness can be obtained. Further, it has been found that when the cBN sintered body is used as a tool base of a cutting tool, the cutting edge is less likely to be chipped even when intermittent cutting is performed in which a large load is applied to the cutting edge.

The present invention has been completed based on the above findings, and is characterized by the following configuration.

(1) The invention of claim 1 is a cBN sintered body comprising cubic boron nitride particles and a ceramic binder phase, wherein WSi having an average grain size of 10nm to 200nm is dispersed in the cBN sintered body so that the content ratio is 1 vol% to 20 vol% or less₂。

(2) Another embodiment of the present invention is a cutting tool comprising the cBN sintered body described in the above (1) as a tool base.

In the cBN sintered body according to the present invention, since the reaction product with the cBN particles, that is, WSi containing no B and N in its constituent components is formed₂The fine particles of (2) are dispersed, so that the generation of a Ti boride phase generated at the cBN particle-binder phase interface is not inhibited, and the progress of cracks generated in the sintered body is made to pass through WSi dispersed in the sintered body without lowering the adhesion of the cBN particle-binder phase interface₂The fine detour exhibits an effect of suppressing the linear progression of the crack and improving the toughness.

Further, the cutting tool according to the present invention uses the cBN sintered body as a tool base, and thus the cutting edge is less likely to be damaged even when interrupted cutting is performed with a large load on the cutting edge, and for example, even in interrupted cutting of high hardness steel, the cutting tool is excellent in wear resistance and has excellent chipping resistance in long-term use.

Drawings

FIG. 1 shows WSi contained in a sintered structure in one embodiment of a cBN sintered body according to the present invention₂Wherein the shape and size of each tissue does not conform to the actual tissue.

FIG. 2 is a diagram showing an example of XRD (X-ray diffraction) of the sintered body 9 of the present invention as a sintered cBN body according to the present invention.

Detailed Description

The present invention will be described in detail below. In the present specification, when a numerical range is expressed by using "-" this range includes upper and lower numerical values.

[ average particle diameter of cBN particles ]

The average particle diameter of the cBN particles used in the present invention is not particularly limited, but is preferably in the range of 0.2 to 8.0. mu.m. Thus, the sintered body contains hard cBN particles, and hence the effect of improving the chipping resistance can be obtained. Furthermore, by dispersing cBN particles having an average particle diameter of 0.2 to 8.0 [ mu ] m in the sintered body, chipping and chipping originating from the uneven shape of the cutting edge caused by the cBN particles falling off from the tool surface during use of the tool are suppressed. Furthermore, by suppressing the propagation of cracks that progress from the interface between the cBN particles and the binder phase or cracks that progress from the breaking of the cBN particles, which are generated by the stress applied to the cutting tip during the use of the tool, it is possible to have excellent chipping resistance.

The average particle diameter of the cBN particles can be determined as follows.

The cross-sectional structure of the cBN sintered body was observed by a Scanning Electron Microscope (SEM) to obtain a secondary electron image. The cBN particle portions in the obtained image were extracted by image processing, and the average particle diameter was calculated from the maximum length of each particle obtained by image analysis. In order to clearly judge the cBN particles and the binder phase in the image at the time of extracting the portions of the cBN particles in the image by the image processing, the binarization processing is performed so that the cBN particles become black by using an image of pixels in which the ratio of the values of the pixels of the cBN particles portion to the values of the pixels of the binder phase portion becomes 2 or more, and displaying the image in a monochrome of 256 gradations with the value of the black pixel in the image set to 0 and the value of the white pixel set to 255.

The region for determining the pixel value of the cBN particle portion or the binder phase portion is determined from the average value in a region of about 0.5. mu. m.times.0.5. mu.m, and preferably, at least the average values determined from different 3 points in the same image are used as the respective references.

In addition, after the binarization process, the cBN particles that are considered to be in contact with each other are separated from each other using a process of separating portions where the cBN particles are considered to be in contact with each other, for example, using watershed (an algorithm of obtaining a region by expanding the center of the region called watershed algorithm/mark toward an adjacent pixel).

The portion (black portion) corresponding to the cBN particles in the image obtained after the binarization process was subjected to particle analysis, and the obtained maximum length was defined as the maximum length of each particle and defined as the diameter of each particle. As a particle analysis for obtaining the maximum length, for example, a value of the larger of two lengths obtained by calculating the Feret diameter with respect to one cBN particle is defined as the maximum length, and this value is defined as the diameter of each particle. The volume obtained by calculation assuming an ideal sphere having the diameter is defined as the volume of each particle, the cumulative volume is determined, and a graph is drawn from the cumulative volume with the vertical axis being the volume percentage [% ]andthe horizontal axis being the diameter [ μm ]. On the graph, the diameter at 50% by volume was defined as the average grain size of cBN particles, and the average value of the three observation regions was defined as the average grain size [ μm ] of cBN. In the particle analysis, the length (μm) of each pixel is set using a value of a scale known in advance by SEM. The observation region used for image processing is preferably a field-of-view region of about 15.0. mu. m.times.15.0 μm when the average particle size of the cBN particles is 3 μm.

[ content ratio of cBN particles in cBN sintered body ]

The content of the cBN particles in the cBN sintered body is not particularly limited, but when the content is less than 40 vol%, the hard material in the sintered body is small, and when the sintered body is used as a tool, chipping resistance may be lowered, and when the content exceeds 78 vol%, voids which become starting points of cracks are generated in the sintered body, and chipping resistance may be lowered. Therefore, in order to further exhibit the effect of the present invention, the content ratio of the cBN particles in the cBN sintered body is preferably in the range of 40 to 78 vol%.

[ WSi dispersed in cBN sintered body₂]

For WSi dispersed in cBN sintered body₂The description is given.

(1) Average particle diameter

WSi₂The average particle diameter of (A) is 10nm to 200 nm. The reason for this range is that WSi in the binder phase tends to occur when the average particle diameter exceeds 200nm₂Since cracks starting from particles are generated and progressed, the toughness of the cBN sintered body is lowered, and if the average particle diameter is less than 10nm, the cracks cannot be finely detoured and the progress thereof cannot be sufficiently suppressed. WSi₂The average particle diameter of (3) is more preferably 10nm to 160 nm.

(2) Contains the ratio of

WSi₂The cBN sintered body is present in a content ratio of 1 to 20 vol%. The reason for this range is that if it is less than 1 vol%, the cracks cannot be finely detoured to sufficiently suppress the progress thereof, and if it exceeds 20 vol%, the amount of the cracks is not sufficient to improve the toughness of the cBN sintered body, and WSi in the sintered body₂Probability of contact with each other increases, adjacent WSi₂WSi which is bonded to be large during sintering₂WSi susceptible to the hypertrophy₂The generation of cracks as starting points lowers the toughness of the cBN sintered body. The content ratio is more preferably 3% by volume or more and 15% by volume or less.

[ method for producing cBN sintered body ]

An example of a process for producing the cBN sintered body excellent in toughness of the present invention will be described below.

(1) Preparation of raw material powder of component constituting binder phase

As the raw material powder constituting the binder phase,preparation of WSi₂Raw materials and a binder phase. As WSi₂Raw Material WSi having an average particle size of 3 μm₂And (3) powder. To make WSi pulverized to a desired particle size₂Raw material powder, WSi₂The powder is filled in a container lined with cemented carbide, for example, together with cemented carbide balls and acetone, and after the container is covered with a lid, the powder is pulverized by a ball mill, and then classified by a centrifugal separator, whereby the median particle diameter D50 where the vertical axis represents the volume percentage and the horizontal axis represents the particle diameter is defined as the pulverized WSi₂The average particle size of the raw material powder is used for obtaining the WSi with the value of 10-200 nm₂Raw material powder. As a main raw material of the binder phase, conventionally known binder phase-forming raw material powders (TiN powder, TiC powder, TiCN powder, TiAl powder) were prepared₃Powder, Al₂O₃Powder).

(2) Pulverizing/mixing

These raw material powders are charged into a container lined with cemented carbide, for example, together with cemented carbide balls and acetone, and then the container is covered with a lid and pulverized and mixed by a ball mill. Next, cBN powder having an average particle size of 0.2 to 8.0 μm, which functions as a hard phase, is added and further ball mill-mixed.

(3) Molding and sintering

Next, the obtained raw powder of the sintered body is molded under a predetermined pressure to prepare a molded body, which is presintered at 1000 ℃, and then loaded into an ultrahigh pressure sintering apparatus, for example, under a pressure: 5GPa, temperature: the cBN sintered body of the present invention is produced by sintering at a predetermined temperature in the range of 1200 to 1600 ℃.

[ CBN tool ]

The cBN-based ultra-high pressure sintered body cutting tool of the present invention, which uses a cBN-based sintered body having excellent toughness as a tool base body, has excellent chipping resistance even in interrupted cutting machining of high hardness steel, for example, and exhibits excellent wear resistance in long-term use.

[ measuring methods of respective numerical values ]

The method of measuring each numerical value specified in the present invention will be explained.

[WSi₂Average particle diameter of]

To measure WSi₂The average particle diameter of (2) was determined by Auger Electron Spectroscopy (hereinafter referred to as AES) to obtain a mapping image of W element and Si element on the cross-sectional structure of the cBN sintered body. In the obtained image, a portion where the W element and the Si element overlap is extracted by image processing, and an average particle diameter is calculated from each particle determined by image analysis.

WSi₂The average particle diameter of (2) is calculated by identifying a portion where W element and Si element overlap each other in one image as WSi from a mapping image of W element and Si element₂The Ferrett diameter of each particle of (a) is defined as the diameter of each particle. From the volume of each particle calculated from the diameter, the cumulative volume was determined in the same manner as in cBN, and from this cumulative volume, the vertical axis was taken as the volume percentage [% ]]The horizontal axis is taken as the diameter [ mu ] m]The diameter at 50% volume percentage was plotted as WSi in one image used for measurement₂The average particle diameter of (3). This process was performed on three images, and the average value was defined as WSi₂Average particle diameter of [ mu ] m]. In performing particle analysis, the length (μm) of each pixel is set using the value of a scale known in advance by AES. The observation region used for image processing is preferably a field of view region of about 5.0 μm × 3.0 μm.

[ WSi in sintered body₂In the content ratio of]

WSi₂The content ratio of the cBN sintered body was calculated by AES from a mapping image of the W element and the Si element to obtain a cross-sectional structure of the cBN sintered body. In one observed image, a portion where the W element and the Si element are overlapped is taken as WSi₂Computing WSi by image analysis using image processing extraction₂The occupied area is calculated to obtain WSi₂The ratio of the active ingredients to the total amount of the active ingredients. The processing is performed on at least three images, and each calculated WSi is calculated₂The average value of the area ratios of (a) to (b) is defined as WSi₂The content ratio of the cBN sintered body was determined. The observation region used for image processing is preferably a field of view region of about 5.0 μm × 3.0 μm.

Example 1

Examples of the present invention are described below.

In the production of the cBN sintered body of the present embodiment, WSi is prepared as a raw material powder for constituting a binder phase₂Powder, for control of WSi₂The particle size of (3) is prepared by pulverizing the powder using a ball mill and then classifying the powder by centrifugal separation to prepare WSi having a desired particle size range₂Raw material powder. That is, WSi having an average particle size of 3 μm was prepared₂The powder is filled into a container lined with cemented carbide together with cemented carbide balls and acetone, the container is covered with a cover, the container is pulverized by a ball mill, the mixed slurry is dried, and then, the slurry is classified by a centrifugal separator, thereby obtaining WSi with an average particle size of 50 to 200nm₂Raw material powder.

Preparation of WSi prepared in advance as described above₂Raw material powder, TiN powder, TiC powder, TiCN powder and TiAl powder with average grain diameter of 0.3-0.9 mu m₃Powder and Al₂O₃The powders were blended so that the content ratio of the sintered cBN particles becomes 40 to 78 vol% when the total amount of the raw material powder for binder phase constitution (the vol% of each raw material powder is shown in Table 1) selected from these raw material powders and the cBN powder as the raw material for the hard phase is taken as 100 vol%, wet-mixed, and dried.

Next, the obtained sintered body raw material powder was press-molded into a diameter at a molding pressure of 1 MPa: 50 mm. times. thickness: 1.5mm, and then maintaining the shaped body under a pressure: presintering at a predetermined temperature within a range of 1000 ℃ in a vacuum atmosphere of 1Pa or less, and then loading into an ultrahigh pressure sintering apparatus under a pressure of: 5GPa, temperature: the sintered cBN 1 to 12 (referred to as sintered cBN 1 to 12) of the present invention shown in Table 2 were produced by sintering at a temperature of 1400 ℃. The heat treatment of the molded article is mainly intended to remove the solvent in wet mixing. In the above-described production step, it is preferable to prevent the raw material powder from being oxidized in the step up to the ultrahigh pressure sintering as in the present example, and specifically, it is preferable to perform the treatment in a non-oxidizing protective atmosphere. Fig. 2 shows an XRD pattern of the sintered body 9 of the present invention.

[ Table 1]

[ Table 2]

For comparison, the following cases were studied separately: (1) does not contain WSi₂In the case (2) grinding WSi by a ball mill is used₂WSi having an average particle diameter outside the range specified in the present invention, which is obtained by classifying a raw material using a centrifugal separator₂In the case of raw material powder, (3) WSi having an average particle diameter within the range specified in the present invention is used₂Raw material powder having WSi outside the range specified in the present invention₂The case of the content ratio. These WSi are prepared₂TiN powder, TiC powder, TiCN powder, TiAl powder, etc. having an average particle diameter of 0.3 to 0.9 [ mu ] m₃Powder and Al₂O₃And (3) powder. The raw material powders for constituting several binder phases selected from these raw material powders (the volume% of each raw material powder is shown in table 3) and cBN powder as a hard phase were wet-mixed, and the obtained mixture was dried. The blending ratio of the both is such that the content of the cBN particles after sintering becomes 58 to 63 vol% when the content of the mixture is 100 vol%.

Then, molded bodies were produced under the same conditions as those of the sintered bodies 1 to 12 of the present invention, heat-treated, and these molded bodies were subjected to ultra-high pressure high temperature sintering under the same conditions as those of the sintered bodies 1 to 12 of the present invention, thereby producing cBN sintered bodies (hereinafter referred to as comparative sintered bodies) 1 to 5 of comparative examples shown in table 4.

[ Table 3]

[ Table 4]

Next, the sintered bodies 1 to 12 of the present invention and the sintered bodies 1 to 5 of the comparative examples produced above were cut into predetermined dimensions by a wire electric discharge machine. Insert bodies made of WC-based cemented carbide having a composition of 5 mass% Co, 5 mass% TaC, and the balance WC, and an insert shape of ISO standard CNGA120408 were manufactured, and the sintered bodies 1 to 12 of the present invention and the sintered bodies 1 to 5 of comparative examples were brazed at brazed portions (corners) of the insert bodies using a brazing filler metal of an Ag alloy having a composition of 26 mass% Cu, 5 mass% Ti, and the balance Ag, and subjected to upper and lower surface and outer periphery polishing and edge grinding, thereby manufacturing the cutting tools 1 to 12 of cBN-based ultra-high pressure sintered bodies of the present invention (referred to as the cutting tools) and the cutting tools 1 to 5 of cBN-based ultra-high pressure sintered bodies of comparative examples (referred to as the comparative tools) having an insert shape of ISO standard CNGA 120408.

Next, the cutting was performed on the present tools 1 to 12 and the comparative tools 1 to 5 under the following cutting conditions, and the tool life (number of interruptions) until the cutting was lost was measured.

< cutting Condition >

Workpiece material: 8 longitudinal grooved round bars equally spaced in the longitudinal direction of carburized and quenched steel (JIS SCM415, hardness: HRC 58-62),

Cutting speed: 200 m/min,

Cutting depth: 0.1mm,

Feeding: 0.1mm/rev

The dry cutting test of the high hardness steel under the above conditions was carried out. The number of interruptions from the cutting edge to the chipping or chipping of each tool was regarded as the tool life, and the presence or absence of chipping or chipping of the cutting edge was confirmed by observing the cutting edge every 500 times. Table 5 shows the results of the above-described cutting test.

[ Table 5]

As is clear from the results shown in table 5, the tool of the present invention has an extended tool life and improved toughness without causing sudden edge chipping of the cutting edge as compared with the comparative tool. The tool of the present invention has excellent wear resistance even in interrupted cutting of high hardness steel, and exhibits an excellent effect of having excellent fracture resistance in long-term use.

Industrial applicability

When used as a tool base for cBN tools, the cBN sintered body of the present invention can be industrially used because it does not cause chipping of the tool base, exhibits excellent chipping resistance in long-term use, can realize extension of tool life, and can realize high performance of a cutting apparatus, and labor saving, energy saving, and cost reduction in cutting.

Claims

1. A cBN sintered body composed of cubic boron nitride particles and a ceramic binder phase, characterized in that,

in the sintered body, WSi having an average particle diameter of 10nm to 200nm is dispersed so as to have a content ratio of 1 vol% to 20 vol%₂。

2. A cutting tool having a tool base body formed of the cBN sintered body as set forth in claim 1.